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I converted my power brakes to manual brakes years ago because the cam in the 406 was too rough for power brakes. They work "OK",....but not fantastic. Lots of pedal pressure for not a lot of stopping. My 427 is in now and in the spring, I plan to drive it as is, but put the brake project on deck next. I'd like to keep the manual set up, but am considering a 7/8 inch master this time. My concern is pedal travel.
Anyone here have 7/8 in master cylinder manual brakes that can comment on brake feel and pedal travel?
Also if anyone has used a brake line pressure gauge could you post your wheel caliper readings. I plan to purchase and test mine, but it would be helpful to know what others are seeing on decent working brakes......manual brakes that is, not power.
Nice reference, thanks for that but I already have the 1 inch bore master as a manual setup would need. Also moved the pushrod to the upper hole for a 5:1 pedal ratio.
Looking for feedback from guys that may have tried a 7/8 inch bore master, mainly for the pedal stroke. I don't want it going all the way to the floor everytime you hit the brakes.
I've been all over the internet looking for info like that, I made a spread sheet that calculates line pressure, and the 576 number validates my spread sheet if I use a pedal ratio of 4.54,....which I also have seen on various sites. I've also seen anywhere between 5 and 5.40 to 1 pedal ratio on various sites, and one vender I called could not confirm even a pedal ratio.. With the pedal installed I can't check, but am positive the push rod is in the upper hole.
Mark Williams site suggests for a panic stop to expect 1200 psi line pressure, which means for a 4.54 pedal ratio and a 1 inch bore master I'd need 210 lbs on the pedal, so roughly both feet with me standing on it. If I use a 15/16 master bore I can get the 1200 psi with 185 lbs on the pedal, and if I go to a 7/8 inch bore, it drops to 160 lbs. which is kind of why I asked if anyone has tried a 7/8 inch bore.
For me power brakes are not an option, but if I can improve what I have,.......you bet I'm going to.
Go ahead and try it, master cylinders are fairly easy to swap out. Please report back on your findings. I have been wondering about the same for my non power brakes.
GM Archive documents show with a 100 lb pedal pressure a line pressure of 576 psi.
I always thought my line pressure was low, but guess not. This is without standing on the brakes on a panic stop, just jacked up in my garage. Wilwood 1" master cylinder. SS everything.
I've been looking into brake pressure guage kits too, and can't seem to find a decent one that fits 5/16-24 bleeder ports,...I assume that's the stock caliper bleeder size.
Anyone suggest a 1500 lbs setup like Wilwood has? Wilwood Pressure Guage
I watched the video a few times, and with only 600 psi how do your brakes feel? Can you lock up all four tires if you tried? During normal driving I feel my brakes are a bit too hard, and I've never been able to lock them up, even when the car had power brakes. To me something is not what it should be.
Last edited by The Money Pit; 12-11-2022 at 08:11 PM.
There is really good guy with a 64 in the C2 section who has done extensive pressure testing and tried different bore master cylinders. I think all the data is in his 64 build thread. I am sure you can find it. As I remember he has all the data you are looking for. His forum name is FLYNAVY30. I will try to look tomorrow.
Curious what master cylinder you fond w a 7/8 bore. Closest I could find is a Wilwood aluminum unit and its a bit pricey (about $350) for an experiment. I wouldn't get too worried about the pedal travel. You can calculate it. Take the bore ratio, invert it, and multiply that by itself. That will give you the pedal travel ratio. If you're moving an inch now, about an inch and a third if you go to a 7/8 master.
I've been looking into brake pressure guage kits too, and can't seem to find a decent one that fits 5/16-24 bleeder ports,...I assume that's the stock caliper bleeder size.
Anyone suggest a 1500 lbs setup like Wilwood has? Wilwood Pressure Guage
I watched the video a few times, and with only 600 psi how do your brakes feel? Can you lock up all four tires if you tried? During normal driving I feel my brakes are a bit too hard, and I've never been able to lock them up, even when the car had power brakes. To me something is not what it should be.
Short answer, yes, but barely. I was always dissatisfied with the rear brake's authority as engineered by Chevy, as were others who posted on this subject. They never seemed to be doing anything much and never locked even with weight transfer. I adapted Wilwood four cylinder front calipers to my back wheels and with a Tilton pressure reduction valve plumbed into the rear was able to get all four to lock up pretty much simultaneously.
With that mod and Hawk pads ,to answer your first question the brakes bite pretty well and the car stops as well as anything else in my garage.
I went out and looked at my gauges thinking maybe to offer them to you for a cheap sale. They have some sort of tapered adapter so I guess they can fit a couple of applications. However one of them appears to be filled with brake fluid, the other didn't seem that way. I have two because I wanted to see the simultaneous front/rear pressure curves. They are from Longacre and if you want to go over to PM's, we can discuss things.
The plan so far is to bypass the factory proportional valve and try the 7/8 bore master. I run 295 55 15 drag radials so I don’t think locking the rear would be a problem. I can add the Wilwood valve if needed.
My concern was pedal travel. I see what looks like a dual master setup. Did you try running just a single 7/8 note master by chance?
The plan so far is to bypass the factory proportional valve and try the 7/8 bore master. I run 295 55 15 drag radials so I don’t think locking the rear would be a problem. I can add the Wilwood valve if needed.
My concern was pedal travel. I see what looks like a dual master setup. Did you try running just a single 7/8 note master by chance?
That's for the Clutch-
With the 7/8" I have more travel-better to be able to modulate. The 1" manual was like an on/off switch.
"Peak braking power comes just prior to lockup and it's the ability to flirt with that limit that makes modulation so important."
"Braking power is always limited by tire traction and virtually any brake can lock up a wheel. However, a wheel that isn’t rotating is also usually a wheel that isn’t contributing any meaningful amount of control.
Aside from certain situations, lockup is exactly what you don’t want. Let me repeat: lockup is usually not a good thing and anyone who argues that their current brakes “can lock up a wheel just fine” is tacitly admitting that they don’t work as well as they could.
Brake modulation is the ability to precisely and accurately control the amount of clamp force on a rotor with a given amount of input.
In other words, it means you can scrub off as much or as little speed as you want without breaking traction — unless, of course, that’s what you’re trying to do.
Peak braking power comes just prior to lockup and it’s the ability to flirt with that limit that makes modulation so important. Whereas a lesser brake might unpredictably vacillate between moderate braking force and lockup — thus, skipping that all-critical peak in deceleration — a brake with excellent modulation will allow you to consistently peg that mark over and over again."
That’s exactly what I was thinking. The ability to control a lock up, not just to be able to cause one. The 7/8 bore should give a much easier pedal during normal driving and also increase brake clamping under panic stops.
I finally got a brake pressure gauge and had a chance to test the front driver side caliper. Looks like 600 psi on normal braking and with both feet on the pedal I can hit 1000 psi. This is with the one inch bore master cylinder.
Plan to test the rear for comparison then make my decision on what direction to go. Two feet on the pedal for a panic stop. One foot on the pedal as a normal stop.
Last edited by The Money Pit; 12-29-2022 at 07:27 PM.
You might try different pads. There are pads that give a lot more stopping power for the same pressure in the caliper. I'm using Cobalt XR-1s on the '64. It's all manual.
Got rear pressure measurements this afternoon and found normal braking to be 500 psi and panic braking to be 800 psi.
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I suspect the proportional valve is limiting the rear by 200 psi and so I am considering bypassing it to get full line pressure to the rear calipers. I want to try that before possibly going to a 7/8 inch bore master cylinder. Norval did this and claimed a vastly improved braking since the rear was now doing more work. In my spread sheet it looks to be roughly 20% more rear brake clamping.
Has anyone else tried this?
Last edited by The Money Pit; 12-30-2022 at 04:16 PM.
On stock calipers the hydraulic fluid will exert equal force at both the front and rear calipers, the pistons on the rear are smaller
(1 7/8 vs 1 3/8), this allows the front to approach lock up before the rear due to the lower grip exerted by the smaller pistons on the pads.
Could it be that you need an 'adjustable proportioning valve' and not a smaller M/C?
On stock calipers the hydraulic fluid will exert equal force at both the front and rear calipers, the pistons on the rear are smaller
(1 7/8 vs 1 3/8), this allows the front to approach lock up before the rear due to the lower grip exerted by the smaller pistons on the pads.
Could it be that you need an 'adjustable proportioning valve' and not a smaller M/C?
If I may, it is actually equal hydraulic pressure (pounds/sq-in) which X the smaller piston area produces less clamping force at the rear. To equalize force front to rear, or balance it better, the proportioning valve would have to reduce the front pressure, which wouldn't be advisable, unless as Money Pit is suggesting, he ups the pressure with a reduced diameter piston.
I addressed getting a more balanced front/rear action differently, by putting front brakes on the rear and a proportioning valve on the rear so that the rears wouldn't lock up first (kind of dangerous when that happens). Also, the proportioning valve I used (Tilton) had a breakpoint, so early onset of pressure at the rear is the same as the front and with increased pressure, the rears ease off.
The rears mount entirely differently, but for me an adapter solved that problem and I dialed the rears down to fairly even balance at the limit. Building the adapter took a fair amount of fooling around so I can't really say what's better and what's not. I ended up reasonably satisfied but one thing I never got around to is measuring stopping distance accurately.
On a 69, the so-called proportioning valve doesn't actually proportion pressure per the measurements I made on my car (see video). It is just a brass block with a slider switch to supposedly block off a failed brake circuit. It is curious that there is a pressure reduction front to rear on Money Pit's car, so maybe on later cars, there actually is some sort of pressure reduction going on. Taking that out of the picture would reduce the front to rear imbalance. Worth some more investigation I would say.
12-07-2022, 12:22 PM
Manual brake rebuild with 7/8 inch master?
